The present invention relates to a new process for the production of elastomeric polyurethane moldings which may be microcellular having a sealed surface layer and an average density of from 0.8 to 1.4 g/cm.sup.3, wherein specific condensation products of ricinoleic acid are used as internal mold release agents.
The production of polyurethane-based moldings having self-releasing properties using so-called internal mold release agents is known (c.f. e.g. U.S. Pat. Nos. 3,726,952, 4,033,912, 4,024,090, 4,058,492 and 4,098,731; and, German Offenlegungsschriften Nos. 2,121,670, 2,427,273 and 3,012,126).
The mold release agents described in these prior publications are particularly suitable for the production of polyurethane-based products with a sealed outer skin since they provide the moldings with good to very good self-releasing properties. Example 7 of U.S. Patent 4,024,090 does describe the use of an ester of a hydroxy group containing polydimethyl siloxane and ricinoleic acid as an internal mold release.
However, in general, these agents do not work as well in the production of high-density microcellular elastomeric polyurethane-based moldings. Such moldings are generally produced by reaction injection molding techniques using highly-active catalyst-containing reaction mixtures of organic polyisocyanates, relatively high molecular weight polyhydroxyl compounds and chain-lengthening agents (c.f. e.g. German Auslegeschrift No. 2,622,951). Thus, the problem in the production of such moldings as to satisfactory self-releasing properties remains.
Thus, an object of the present invention was to provide internal mold release agents which are suitable for the mass production of elastomeric moldings (which can be microcellular) with self-releasing properties. This object was achieved according to the invention herein by using specific condensation products of ricinoleic acid with mono- and/or poly-valent alcohols as internal mold release agents. The particularly good suitability of the mold release agents essential to the invention herein was surprising in view of the teachings as provided by German Offenlegungsschrift No. 2,121,670 (British Pat. No. 1,365,215) and German Offenlegungsschrift No. 2,404,310 (U.S. Pat. No. 4,058,492).
German Offenlegungsschrift No. 2,121,670 describes binary and ternary mixtures used as mold release agents in the production of preferably rigid molding foams. Hydroxyl group-containing esters of monocarboxylic acids inter alia are described as being useful as mold release components in the aforementioned mixtures. Long-chain fatty and oleic acids on the one hand and various alcohols on the other are used as components for these esters. The list of suitable fatty acids or oleic acids includes ricinoleic acid. The achievement of the objects of the present invention must, however, be regarded as surprising in view of this disclosure, since (i) the production of elastomeric moldings having high density is not mentioned, (ii) the aforementioned esters should only be used as components in binary or ternary mold release agent systems, and (iii) if ricinoleic acid is used, an alcohol is not necessary.
German Offenlegungsschrift No. 2,404,310 recommends the use of free carboxyl group-containing reaction products of ricinoleic acid with long-chain fatty acids, including free carboxyl group-containing polyricinoleic acids (as may be obtained by autocondensing ricinoleic acid) as internal mold release agents in the production of molded foams of the most varied type. These carboxyl group-containing mold release agents have, however, limited suitability for highly-active systems used in reactive injection molding techniques for the production of elastomeric moldings of high density, since they disturb the sensitive catalysis of these systems. Elastic molded foams of high density having good self-releasing properties can be produced with the mold release agents disclosed by this publication, but unfortunately, the interior walls of the molds have to be cleaned after short intervals of time, since the self-releasing properties otherwise disappear after a few reaction cycles. This is obviously due to the moldings not completely reacting on the surface within the requisite short reaction times, with the result that impurities form on the interior wall of the mold after a few reaction cycles. These impurities rapidly suppress the releasing effect of otherwise good mold release agents.